Debugging code which deploys DBI: no logfile, no trace. What's a cause?

[Plymouth Rock <Tr...@newmail.ru>]

http://perl.apache.org/docs/1.0/guide/databases.html#Debugging_code_which_de
ploys_DBI

  PerlSetEnv DBI_TRACE "3=/tmp/dbitrace.log"
  PerlModule Apache::DBI

 I tried mod_perl scripts accessed to DB and
SELECTed some data. But logfile still doesn't
appear. The order and placement the directives
are the same as mentioned in the guide. I'm
sure in settings of Apache2.0.55 + mod_perl2.0.2
+ PostgreSQL8.1; DBI and DBD::PgPP are installed,
Apache::DBI was installed and turned according
to its docs, but I suspect a problem just in it.
Any ideas?